1. Field of the Invention
The present invention relates to apparatus useful for the production of sodium bicarbonate. More particularly, it relates to apparatus for production of sodium bicarbonate which has a simple structure and can be easily operated, and which possesses the advantages that it can be operated in a manner such that the coefficient for absorption of carbon dioxide gas is relatively high and so that the sodium bicarbonate crystals produced will have very desirable particle size.
2. Description of the Prior Art
Heretofore, a Solvay tower has been used in the ammonia soda process for crystallization of sodium bicarbonate, wherein ammonia is absorbed in a brine to obtain an ammoniacal brine and sodium bicarbonate is produced by reacting carbon dioxide gas with the ammoniacal brine. Alternatively, the tower is used in a process for coproduction of ammonium chloride and sodium bicarbonate wherein ammonia and sodium chloride are added to a mother liquor which has been produced by separating sodium bicarbonate crystals therefrom. Ammonium chloride then is crystallized and carbon dioxide gas is absorbed in the mother liquor produced by separating the resultant ammonium chloride resulting in crystallization of sodium bicarbonate.
The Solvay tower comprises many reaction zones which are vertically assembled. Each reaction zone has many partitions, each of which has its perforations covered with a cap so as to prevent free passage of carbon dioxide gas and to ensure good contact of the carbon dioxide gas with the mother liquor produced by the precipitating ammonium chloride (hereinafter referred to as the separated mother liquor).
The separated mother liquor is fed into the top of the tower and carbon dioxide gas is fed from the bottom of the tower, whereby the separated mother liquor is counter-currently contacted with carbon dioxide gas to crystallize sodium bicarbonate. In this manner of production of sodium bicarbonate, the size of the resultant sodium bicarbonate crystals increases with rising temperature. On the other hand, it is preferred to use lower temperatures in order to increase the coefficient for absorption of carbon dioxide in the reaction. Accordingly, in order to produce large sodium bicarbonate crystals, the separated mother liquor should be fed into the Solvay tower at a relatively high temperature. However, the separated mother liquor fed into the tower reacts with carbon dioxide gas while descending. As a result, the heat of the ensuing reaction causes the temperature of the gas to rise whereby the growth of sodium bicarbonate crystals is improved but the coefficient for absorption of carbon dioxide gas in the reaction is decreased. Consequently, many cooling tubes for controlling the temperature are generally assembled near the bottom of the tower whereby the temperature in the tower can be controlled below a predetermined temperature. Unfortunately, a scale consisting of a large amount of sodium bicarbonate crystals adheres to the cap used on the perforations, to the inner wall of the tower and to the outer wall of the cooling tubes so as to clog up the inner part of the tower. This disadvantageous phenomenon cannot be prevented. As a result, in industrial operation, several Solvay towers are required so that they may be alternated in use for removing the scale. Heretofore, this has been a practical necessity, making the operation complicated. Also, the apparatus has a complicated structure and it is correspondingly expensive. Moreover, when a large Solvay tower is designed to increase the production for a single tower, a large amount of additional equipment such as cooling apparatus, is required, further disadvantageously increasing the cost. Consequently, there continues to exist a need for a new apparatus for production of sodium bicarbonate which is free from these disadvantages.